1. Field of the Invention
The present invention relates to video display technology.
2. Description of the Related Art
The popularization of video display apparatuses such as TV receivers in recent years has led to the advent of video display apparatuses having various resolutions (pixel counts) for the display region. There are also video display apparatuses that differ in the type of video signal that can be displayed despite having the same resolution. This is due to information on displayable video signals such as vertical scanning frequency, effective pixels and blanking period being set on a per video display apparatus basis.
Identification information (compatible video signal information) of displayable video signals including resolution, vertical scanning frequency, effective pixels and blanking period is typically stored in respective storage areas of the video display apparatuses. For example, the Digital Visual Interface (DVI) standard defines a source apparatus (video output apparatus) and a sync device (video display apparatus), with compatible video signal information being included in Extended Display Identification Data (EDID) on the sync device side. The source apparatus, by obtaining EDID from the sync device, can ascertain the video signals that are displayable by the sync device. That is, in order to ensure that video signals compatible with the video display apparatus are output from the video output apparatus, such information on compatible video signals needs to be transmitted to the video output apparatus.
However, while displayable video signals differ depending on factors such as resolution and settings even with the same video display apparatus, not all combinations can be included in the compatible video signal information in view of the storage area, and description is divided into detailed description of a prescribed number of video signals and simplified description of resolutions, frequencies and the like. If a video signal that is not described in the detailed video signal setting information needs to be received due to a change in video display apparatus settings or the like, detailed video signal setting information is generated and rewritten, using corresponding information included as the simplified video signal description. In the case of generating detailed video signal setting information from information included as simplified video signal description, information such as pixel clock and blanking period is generated using a prescribed calculation formula set in a standard.
For example, in the above-mentioned DVI standard, a Detailed Timing (DT) area as an area describing detailed video signal setting information, an Established Timing (ET) area as an area describing simplified video signals, and a Standard Timing (ST) area are defined within EDID. Japanese Patent Laid-Open No. 2008-252819 discloses a technique for obtaining an optimal video signal by rewriting EDID, in the case where settings such as image quality and resolution of the TV receiver serving as a video display apparatus differs from normal settings.
However, the technique of Japanese Patent Laid-Open No. 2008-252819 is directed to rewriting the identification information of displayable video signals in the case where the settings of the video display apparatus are changed, and does not determine whether the video output apparatus is capable of outputting a compatible video signal. That is, if information on a compatible video signal of the video display apparatus that has been rewritten with reference to only the settings of the video display apparatus is transmitted, an incompatible video signal could possibly be output from the video output apparatus.